Don’t tell Miki Agrawal that Thinx, her line of underwear designed to let women menstruate freely without tampons or pads, might not be for everybody. Agrawal fiercely believes -- to quote Thinx’s tagline -- that these panties are “for women with periods.” Meaning: all of them. “Girls are sick of wearing tampons,” Agrawal says. “As a woman, how many pairs of our underwear have we all ruined from monthly accidents?”

She might be right: Since a big market push last spring, she says she’s sold “tens of thousands” of pairs of Thinx, which look like normal underwear. According to Agrawal (and a few enterprising bloggers), they feel like regular underwear, too. But unlike your daily underpants, these are antimicrobial, moisture-wicking, liquid-absorbing garments that took three and a half years to develop. They come in six styles, cost from $24 to $38 each and promise to hold up to two tampons’ worth of fluid.

For women in the U.S., Agrawal pitches this as a low-cost luxury item. For women in developing countries, it could be the key to keeping girls in school. While visiting South Africa in 2010, Agrawal met a young girl who wasn’t attending class. “She said, ‘It’s my week of shame,’” Agrawal recalls. “Girls in the developing world have a ‘period problem,’ too, but access to nothing.” So for every pair of Thinx sold, the company donates to AfriPads, a Uganda-based company that makes reusable pads and employs local women. Agrawal will also launch a nonprofit arm this year, with plans to open 10 safe, empowering “Girls Clubs” across Africa.

Agrawal sees Thinx’s mission as sociopolitical. “There’s a true shift in ‘period feminism,’ moving away from using a product invented by men in 1931,” she says, referring to the year Tampax first hit the market. That hints at Thinx’s next product, of which she won’t say much, just that it will “disrupt the category and the sustainability problem of the 20 million tampons and pads that go into landfills every year.” She has also launched a line of low-cost, attachable bidets, and underwear for incontinence is up next on her brave to-do list.